Immunity to infections with the eimeria has been the subject of a number of recent reviews. 1-3 These cover in detail much of the literature upon which our current understanding is based. For this reason, the approach chosen here is deliberately selective. We have decided to concentrate only on those aspects of the host response which can be correlated directly with resistance to infection, and have focused primarily on work published since 1984. Our objective is threefold: (1) to place the topic of immunity to eimeria in the wider context of immunoparasitology, drawing out significant similarities with, as well as differences from, responses to other parasites; (2) to define the capacity of the host to mount protective responses at the site of infection, concentrating upon the intestine, and (3) to draw from recent papers the basis for a model to explain immunity to eimeria which may help to define and focus future research.